One of the obvious reasons for using mixtures of active ingredients is the different sensitivities of the individual pests to the used chemicals and it is often cheaper, simpler or more efficient to use the suitably combined mixtures on one single occasion (J. Stored Prod. Res., 1977, Vol. 13. 129-137; Pestic. Sci., 1983. 14 385-398; Pestic. Sci., 1983. 14 373-384; JP PS 50 58237(1975)1973;(54 95730) (1979/1978); 54 92625; 53 62830 (1970)1976).
It is known that the absorbed pyrethroids are made ineffective by the insects through different mechanisms. One of these detoxification methods is realized by esterases: by splitting the ester bond, the pyrethroid hydrolyzes to a non-toxic molecule. The phosphate esters inhibit certain variations of enzymes metabolizing pyrethroids.
The esterases are different with regard to species localization substrate-specific character and kinetic parameters. The inhibitor activity of certain esterase inhibitors is consequently different. Thus if on one species, an esterase inhibitor influences the metabolism of a given, pyrethroid one cannot tell the possible interaction of another species or another pyrethroid molecule.
Thus, for instance, the insecticide pro feno fos effectively inhibiting enzymes hydrolyzing permethrin, cypermethrin does not effect the activity of pyrethroids measured on Tribolium castaneum grubs (Pestic. Biochem. Physiol., 1980, 14 81-85, Pestic. Sci., 1983 14 367-372).
A further example of the contradictory results is that the insecticide chlorpyriphos acts as a synergist for flycitrinate and fenvalerate on Spodoptera littoralis but it acts as an antagonist the toxicity of cypermethrin (BCPC Proceedings Vol. 3:943). Against the same species monocrotophos, pro feno fos, azinphos-methyl and acephate act as a synergistic agent in a broad combination range together with cypermethrin, fenvalerate and deltamethrin. The following combinations are exceptions: fenvalerate+azinphos-methyl, deltamethrin+azinphos-methyl and deltamethrin+pro feno fos double mixtures (Phytoparasitica 1986. 14/(2):101) which show an additive or antagonist interaction. The synergism could be shown only by oral administration of the active ingredients, the topical tests were without any result.
Against field resistance a successful result can be expected with those combinations where between the activity of the individual components a negative cross-correlation can be observed. One of the less thoroughly examined mixtures is the mixture of fenvalerate and azinphos-methyl and a negative cross-correlation against spider mites (Tetranychus urticae) is disclosed in Nature 1979 281:298. The 1:1 mixture of the two active ingredients resulted in a favorable activity against sensitive and resistant spider mites (Pestic.Sci., 1980 11:600).
According to the DBP 27 57 768 mixtures containing permethrin as one component and bromophosethyl, chlorpyriphos, bromphos, malathion and diazinon as a second component showed an antagonist interaction in the laboratory against the normally sensitive house fly (Musca domestica), but on harvested and resistant populations the LD.sub.50 value which is one order of magnitude higher, showed a de facto synergism. On Christoneura occidentalis belonging to the order of Lepidoptera chlorpyriphos showed a synergistic effect with deltamethrin at a ratio of 10:1 but acted as an antagonist to permethrin and fenvalerate (J.Econ.Entomol., 1984. 77 16-22) whereas on another Lepidoptera species (Ostrinia nubialis) the combination of permethrinchlorpyriphos showed a significant synergism within a wide combination range (J.Econ.Entomol., 1982 75 28-30).
It may occur that synergism may be observed on the sensitive strain and on the already resistant strain antagonism can be observed. As an example for this effect the interaction of cypermethrin and monocrotophos on Spodoptera littoralis can be mentioned. See Med.Fac.Landbouw.Rijksuniv.Gent, 50/2b, 1985 751.
The abbreviations used in the tables of this specification are as follows:
CIP=Cypermethrin=Alpha-cyano-3-phenoxybenzyl-3-(2,2-dichlorovinyl)-2,2-dime thyl-cyclopropane-carboxylate PA0 CHX="chinmix"=out of the possible isomers of cypermethrin a 40:60 mixture of 1RcisS+1ScisR:1RtransS+1StransR isomers PA0 TRX=transmix=out of the possible isomers of cypermethrin a 50:50 mixture of 1RtransS:1StransR isomers PA0 QUI=quinalphos=0,0-diethyl-0-quinoxalin-2-yl phosphorothioate PA0 DIA=diazinon=0,0-diethyl-0-2isopropyl-6-methylpyrimidine-4-yl-phosphorothio ate PA0 TRIA=triazophos=0,0-diethyl-0-1-phenyl-1H-1,2,4-triazole-3-yl-phosphorthioa te PA0 MET=methidathion=S-2,3-dihydro-5-methoxy-2-oxo-1,3,4-thiadiazol-3-yl-methyl -0,0-dimethyl-phosphorodithioate PA0 HEPT=heptenophos=chlorobicyclo3,2,0hepta-2,6-dien-6-yl-dimethyl-phosphate PA0 PHOS=phosalone=S-6-chlor-2,3-dihydro-2-oxobenzoxazol-3-yl-methyl 0,0-diethyl-phosphorodithioate PA0 SF=synergistic factor PA0 PBO=piperonyl-butoxide PA0 phosphoric acids: phosphamidon, heptenophos, tetrachlorvinphos, dichlorvos, trichlorphon, propetamphos PA0 thiophosphoric acids: parathion, methylparathion, fenitrothion, diazinon, triazophos, pirimiphos-ethyl, pirimiphos-methyl, demeton, mevinphos, quinalphos, fenthion, bromophos, coumaphos, ethoprop, cyanophos PA0 dithiophosphates: malathion, mephospholan, phormothion, phenthoate, phosmet, methidathion, phosalone, sulprofos. PA0 Solvesso 100 (99% of aromatic content, 90% of C.sub.9 -alkyl-benzene) PA0 Solvesso 150 (99% of aromatic content, 85% of C.sub.10 -alkyl-benzene). PA0 Shellsol A, Aromasil H and Aromatol are also suitable.